An overwhelming majority of Israelis entitled to vote in the US presidential election have cast their ballot for Mitt Romney, according to a poll conducted by an organisation aimed at maximising turnout.

Eighty-five percent of the 80,000 American-Israelis who registered to vote through iVoteIsrael backed the Republican candidate, the survey indicated. The organisation claimed that in states where the race is tight, expatriate voters from Israel could make a significant difference. Around 7,500 Israelis are registered to vote in Florida, and 3,500 in Ohio.

But Democrats Abroad Israel dismissed the poll as "slanted and extremely partial" because it was based on surveys carried out only at polling stations set up by iVoteIsrael. The acting chairman Hillel Schenker told the Israeli newspaper Haaretz: "All they're doing is providing information about the people they polled at their polling stations, in places where there are predominantly Orthodox and rightwing Jews."

The campaign group says it is non-partisan and its only interest is to maximise the vote among eligible Israelis. It said voter participation had quadrupled from the 20,000 Israelis who voted in 2008, and that between 20% and 25% of all overseas votes this year would come from Israel.

Israel's prime minster, Binyamin Netanyahu, has been accused of favouring a Romney victory in next week's election. Relations between Netanyahu and Barack Obama have been severely strained over the issue of the Iranian nuclear programme. Romney is perceived to be more sympathetic to Netanyahu's view that military action may be needed to halt the programme.

Romney has consistently sought to portray Obama as failing to maintain the traditionally close ties between the US and Israel. Almost eight in 10 Jewish Americans voted for Obama in 2008, and a majority are expected to vote Democrat in this election.